1. Field of the Invention
The present invention relates to materials that can be used to splice or connect the ends of optical glass fibers of differing compositions.
2. The Prior Art
Optical glass fibers and devices used in the telecommunications industry traditionally have been made of silica based compositions. Fluoride glasses, and notably those based upon fluoro-zirconates, have also been developed for telecommunications applications. It has been demonstrated that these materials possess fundamental advantages over silica-based materials for certain applications. Currently, the most commercially promising application for fluoride glasses involves their use as a host for Praseodymium (Pr) in fiber-based optical amplifiers.
Telecommunication devices based upon fluoride glass fibers must be efficiently likable to single mode silica glass fiber, the standard fiber for telecommunications. However, there are fundamental differences between silica and fluoride glasses which tend to make them incompatible in an optical system or assembly. Fluoride glasses typically exhibit glass transition (T.sub.g) values between 200.degree. C. and 300.degree. C. and exhibit onset of devitrification (crystallization) at temperatures usually above 100.degree. C. above T.sub.g. In contrast, silica possesses a T.sub.g of 1000.degree. C. to 1100.degree. C. and a marked resistance to devitrification. Such a large difference in maximum usable temperature renders the common fusion splice method for connecting silica fibers to one another impractical for mating silica and fluoride fibers. It is imperative, therefore, to have a low temperature fixative for the splice between the fluoride and silica fibers.
Commercially available, organic fixatives are low temperature but tend to degrade under the power levels required for device operation and typically are prone to moisture absorption. Such behaviors make these materials less than appealing for long life telecommunication applications involving high laser power levels. In addition, many organic fixatives absorb strongly in the blue region of the visible spectrum, and a significant amount of blue, up-converted light is generated in the Pr-doped fluoride fiber amplifier.